I'll add another datapoint to this discussion. Sometimes the AC performance can decline very slowly and might not be very noticeable. If you have access to a thermometer, check each side of the vents with the AC on high. If there is any more than a slight difference in values, you probably have low refrigerant/leaking evaporator. The leak will cause a bad odor.

that's exactly what happened to my car, that's exactly what I was trying to explain above... it can take a year before it get noticeable...